Fans of this type must satisfy various requirements, including: low noise level, high efficiency, compactness, capacity to achieve good pressure and flow rate values. In particular, achieving good general performance while keeping noise levels down requires careful design of the blades and the profiles of which they consist. A fan of this type is known from U.S. Pat. No. 6,241,474, which describes a low noise fan with blades whose angle or pitch decreases gradually from the hub to the tip over a predetermined extension of the radius, then their angle increases again towards the tip. The blades are connected to one another by an external ring.